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de Reus K, Carlson D, Lowry A, Gross S, Garcia M, Rubio-Garcia A, Salazar-Casals A, Ravignani A. Vocal tract allometry in a mammalian vocal learner. J Exp Biol 2022; 225:275049. [PMID: 35483405 PMCID: PMC9124484 DOI: 10.1242/jeb.243766] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2021] [Accepted: 03/14/2022] [Indexed: 11/20/2022]
Abstract
Acoustic allometry occurs when features of animal vocalisations can be predicted from body size measurements. Despite this being considered the norm, allometry sometimes breaks, resulting in species sounding smaller or larger than expected for their size. A recent hypothesis suggests that allometry-breaking mammals cluster into two groups: those with anatomical adaptations to their vocal tracts and those capable of learning new sounds (vocal learners). Here, we tested which mechanism is used to escape from acoustic allometry by probing vocal tract allometry in a proven mammalian vocal learner, the harbour seal (Phoca vitulina). We tested whether vocal tract structures and body size scale allometrically in 68 young individuals. We found that both body length and body mass accurately predict vocal tract length and one tracheal dimension. Independently, body length predicts vocal fold length while body mass predicts a second tracheal dimension. All vocal tract measures are larger in weaners than in pups and some structures are sexually dimorphic within age classes. We conclude that harbour seals do comply with anatomical allometric constraints. However, allometry between body size and vocal fold length seems to emerge after puppyhood, suggesting that ontogeny may modulate the anatomy–learning distinction previously hypothesised as clear cut. We suggest that seals, and perhaps other species producing signals that deviate from those expected from their vocal tract dimensions, may break allometry without morphological adaptations. In seals, and potentially other vocal learning mammals, advanced neural control over vocal organs may be the main mechanism for breaking acoustic allometry. Summary: Harbour seals are vocal learners that can escape acoustic allometry despite complying with anatomical allometric constraints. Advanced neural control over their vocal organs may allow them to break acoustic allometry.
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Affiliation(s)
- Koen de Reus
- Comparative Bioacoustics Group, Max Planck Institute for Psycholinguistics, 6525 XD Nijmegen, The Netherlands.,Artificial Intelligence Lab, Vrije Universiteit Brussel, 1050 Brussels, Belgium.,Research Department, Sealcentre Pieterburen, 9968 AG Pieterburen, The Netherlands
| | - Daryll Carlson
- Research Department, Sealcentre Pieterburen, 9968 AG Pieterburen, The Netherlands.,Department of Earth System Science, Stanford University, Stanford, CA 94305-4216, USA
| | - Alice Lowry
- Research Department, Sealcentre Pieterburen, 9968 AG Pieterburen, The Netherlands.,School of Environmental Sciences, University of Liverpool, Liverpool, L3 5DA, UK
| | - Stephanie Gross
- Institute for Terrestrial and Aquatic Wildlife Research (ITAW), University of Veterinary Medicine Hannover, Foundation, 25761 Büsum, Germany
| | - Maxime Garcia
- Animal Behaviour, Department of Evolutionary Biology and Environmental Studies, University of Zurich, 8057 Zürich, Switzerland.,Center for the Interdisciplinary Study of Language Evolution, University of Zurich, CH-8050 Zürich, Switzerland
| | - Ana Rubio-Garcia
- Research Department, Sealcentre Pieterburen, 9968 AG Pieterburen, The Netherlands
| | - Anna Salazar-Casals
- Research Department, Sealcentre Pieterburen, 9968 AG Pieterburen, The Netherlands
| | - Andrea Ravignani
- Comparative Bioacoustics Group, Max Planck Institute for Psycholinguistics, 6525 XD Nijmegen, The Netherlands.,Research Department, Sealcentre Pieterburen, 9968 AG Pieterburen, The Netherlands.,Center for Music in the Brain, Department of Clinical Medicine, Aarhus University & The Royal Academy of Music Aarhus/Aalborg, 8000 Aarhus C, Denmark
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